Python DeltaTest — Intelligent Test Selection for VS Code

Run only the tests affected by your code changes — with inline coverage glow and auto-refresh.

Delta is an intelligent test runner that maps every line of your source code to the exact tests that cover it. When you change code, Delta instantly knows which tests to run — and which ones to skip.

This VS Code extension brings Delta directly into your editor with inline coverage visualization, live test highlighting, and a built-in control panel.

Getting Started

1. Install the Delta CLI

Install the command-line utility inside your active virtual environment:

pip install pytest-deltatest

2. Build Your Mapping Database

Run your tests once to build the initial coverage mapping database:

# Build mapping with subprocess coverage tracking (recommended)
delta build-mapping --subprocess

This creates .delta/test_mapping_<branch>.db in your project root. Be sure to add .delta/ to your .gitignore.

3. Open VS Code & Enjoy Smart Coverage

Open your project in VS Code. The extension will automatically find your mapping database and display soft, color-coded highlights directly behind the covered lines. Hover over any covered line to see exactly which tests execute it.

4. Run Affected Tests

Whenever you make changes, click the Run Affected Tests button in the Delta panel (or run delta run / pytest --delta in your terminal). Only the tests covering your modified lines will run, finishing in seconds instead of minutes!

Features

Inline Coverage Glow

Every line covered by at least one test gets a soft, color-coded glow directly in your editor. Hover over any line to see a list of the exact tests covering it.

Interactive Control Panel

Directly inside VS Code's sidebar settings view, you can:

• Update Mapping (delta build-mapping && delta push)
• Run Affected Tests (delta run) with real-time test outcomes captured directly in VS Code's Test Results panel and output streamed to the Delta Auto-Run output channel.

Auto-Refresh

The extension watches your mapping database and updates the editor highlights automatically after every test run.

Configuration

Links

• Website: deltatest.dev
• Documentation: deltatest.dev/docs